xleoken commented on code in PR #2119:
URL:
https://github.com/apache/incubator-celeborn/pull/2119#discussion_r1413278837
##########
master/src/main/scala/org/apache/celeborn/service/deploy/master/Master.scala:
##########
@@ -666,23 +666,32 @@ private[celeborn] class Master(
val shuffleKey = Utils.makeShuffleKey(requestSlots.applicationId,
requestSlots.shuffleId)
val availableWorkers = workersAvailable()
+ // reply false if all workers are unavailable
+ if (availableWorkers.isEmpty) {
+ logError(
+ s"Non available workers, offer slots for $numReducers reducers of
$shuffleKey failed!")
+ context.reply(RequestSlotsResponse(StatusCode.SLOT_NOT_AVAILABLE, new
WorkerResource()))
+ return
+ }
+
val numAvailableWorkers = availableWorkers.size()
val numWorkers = Math.min(
Math.max(
if (requestSlots.shouldReplicate) 2 else 1,
if (requestSlots.maxWorkers <= 0) slotsAssignMaxWorkers
else Math.min(slotsAssignMaxWorkers, requestSlots.maxWorkers)),
numAvailableWorkers)
+
+ // We treated availableWorkers as a Circular Queue here.
val startIndex = Random.nextInt(numAvailableWorkers)
+ val endIndex = startIndex + numWorkers
+
val selectedWorkers = new util.ArrayList[WorkerInfo](numWorkers)
- selectedWorkers.addAll(availableWorkers.subList(
- startIndex,
- Math.min(numAvailableWorkers, startIndex + numWorkers)))
- if (startIndex + numWorkers > numAvailableWorkers) {
- selectedWorkers.addAll(availableWorkers.subList(
- 0,
- startIndex + numWorkers - numAvailableWorkers))
+ for (index <- startIndex until endIndex) {
+ val realIndex = index % numAvailableWorkers
+ selectedWorkers.add(availableWorkers.get(realIndex))
}
+
Review Comment:
hi @mridulm, thanks for your detail response 👍, you are very correct about
the algorithm performance itself, and I learned about performance testing
framework from your suggestion.
As we known, celeborn is designed for remote shuffle, which usually used in
OLAP scenarios, so that the small performance gap is acceptable from my side,
and the focus of this patch is to improve readability.
and we can see that there is a similar algorithm in the
`Master#handleRequestSlots`.
https://github.com/apache/incubator-celeborn/blob/1c7cd1bd1392c8d3fd4396c539696dc79835f8dc/master/src/main/scala/org/apache/celeborn/service/deploy/master/Master.scala#L738-L750
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